MontanaWay wrote:has anyone here used the KT150 in an M125 or even ST120, (< which might be total overkill), and if yes, what are your thoughts?

I have had a few customers use the Tung-Sol KT150 in the VTA ST-120 and the VTA M-125 amps. They should be biased AS A KT88 in these amps. The problem with them is that they are expensive @ about $100 a tube or $400 per quad. They don't really offer anything in the way of better sound or "more power" being biased as a KT88. The Tung-Sol KT120's are almost half the price at maybe $55 per tube and work really well in the ST-120 and M-125. In both of these amps, the KT120 offers about an 8% increase in power due to the larger plates (than a KT88) and their ability to transfer more electrons per second than a KT88. I am sure that the KT150's would be about the same and "possibly" add a little more power when used in KT88 based amps like the ST-120 and M-125's. To take real advantage of the KT120 and KT150 output tubes, you would probably have to get the plate voltages above 600 volts and run the bias at 100+ milliamps per tube. Some say that a PAIR of KT150's can produce 200+ watts but I have my doubts .. The only commercial amp that I know of that uses KT150's is the Ayon Sprit 3 from Austria. Yes - They show the amp with KT150's plugged in but they also state that the amp produces just 2 X 80 watts in the pentode mode - SO - they are using this tube "as a KT88" ... See link below ...

holy smokes!!...the prices on these Ayon's....I could utter a lot of expletives......but I shall refrain!One would at the VERY least expect that they would use the full potential of the KT150's...especially at those astronomical prices!I have yet to find a circuit for an amp 'dedicated' to the KT150's quoted abilities, I shall keep searching.

MontanaWay wrote:holy smokes!!...the prices on these Ayon's....I could utter a lot of expletives......but I shall refrain!One would at the VERY least expect that they would use the full potential of the KT150's...especially at those astronomical prices!I have yet to find a circuit for an amp 'dedicated' to the KT150's quoted abilities, I shall keep searching.

I wouldn't want an amp 'dedicated' to a proprietary tube made by a single manufacturer. What if that single tube-maker went gunny-bag?

Funny looking KT150's ... also rated at 80wpc, which doesn't even touch the potential ... looks like some beefy iron, but hard to tell with a potted xformer.

And for only $5K!

thats what I don't get...see plenty of amps using the KT150, but most are under 100W.....can get away with the KT120 and even KT88 in a lot of cases...I guess they use the KT150 so that they can add $3K to the price!!!!!!

I know this is an older thread, but just to update, as I would purchase the M125 if offered with an updated transformer/cap that would give the benefits of KT150 tube use.

I have read a lot about the KT150 and the most talked about improvement is not the power increase, but the sonic improvements... most agree that the KT150 takes the best of the EL34/6550/KT88/KT120 tubes and packages it into the KT150.

There is also the benefit of fewer tubes in the chain to get more power, resulting in less noise/better sound.Another benefit, as seen in the amps below, is flexibility of using MANY different tubes.

The Quicksilver 120 mono's are using just 2 output tubes getting 120 watts:http://www.quicksilveraudio.com/products/Mono%20120.html

What they don't tell you is that to get 120 watts out of TWO KT88's or KT150 output tubes you have to run those output tubes really hard. The Quicksilver 120 mono's are probably running a B+ of maybe 630 VDC to get those power levels out of just TWO output tubes. KT150's will take the 600+ B+ but a modern KT88 will probably have a short life in that amp. The M-125's run the output tubes at a more comfortable 500 VDC and the output tubes will last longer. Consider also that each KT150 output tube costs $100 and that a KT88 costs $50 - so using two KT88's @ 500 VDC B+ gives the same power and also costs about the same.

Also consider that a pair of wired and tested Quicksilver 120 mono's with two KT150 output tubes costs $4395 and a pair of wired and tested M-125's with all tubes and about the same power costs $2795 - a savings of $1600. You can save even more if you build the M-125's from kits ...